Encapsulation of solar cells

ABSTRACT

The present invention comprises a solar cell module and a method of encapsulating the module. The solar cell module comprises a rigid or flexible superstrate and/or substrate having one or more solar cells, and an encapsulent which is a cured liquid silicone encapsulant. The encapsulant composition preferably comprises a liquid diorganopolysiloxane having at least two Si-alkenyl groups per molecule, a silicone resin containing at least two alkenyl groups; a cross-linking agent in the form of a polyorganosiloxane having at least two silicon-bonded hydrogen atoms per molecule, in an amount such that the ratio of the number of moles of silicon-bonded hydrogen to the total number of moles of silicon-bonded alkenyl groups is from 0.1:1 to 5:1; and a hydrosilylation catalyst, preferably a platinum based catalyst. The continuous solar cell module encapsulation process comprising the steps of uniformly applying by spraying, coating or dispensing a predetermined volume of a liquid silicone encapsulant onto a solar cell module and curing said encapsulant thermally or by infrared radiation. The preferred method of applying the liquid silicone encapsulant on to the solar cell modules is by means of a curtain coater.

This invention relates to a solar cell and a process of applying asilicone based encapsulant material onto solar cells to form a solarcell module.

Solar or photovoltaic cells are semiconductor devices used to convertlight into electricity (referred to hereafter as solar cells). Typicallyupon exposure to light, a solar cell generates a voltage across itsterminals resulting in a consequent flow of electrons, the size of whichis proportional to the intensity of the light impinging on thephotovoltaic junction formed at the surface of the cell. Solar cells canbe made from any suitable semiconductor materials such as for example,crystalline or polycrystalline silicon or thin film silicon, e.g.amorphous, semi crystalline silicon, gallium arsenide, copper indiumdiselenide, cadmium telluride, copper indium gallium diselenide,mixtures including any one or more of the latter and the like. There aregenerally currently two types of solar cells, wafers and thin films. AWafer is a thin sheet of semiconductor material made by mechanicallysawing it from a single crystal or multicrystal ingot or casting. Thinfilm based solar cells are continuous layers of semi-conductingmaterials typically deposited on a substrate or superstrate bysputtering or chemical vapour deposition processes or like techniques.

Because of the fragile nature of both the wafer and thin film basedsolar cells it is essential for the cells to be supported by a loadcarrying supporting member. This load carrying supporting member may berigid, e.g. a glass plate rigid material, or a flexible material e.g. ametallic films and/or sheets or suitable plastic materials such aspolyimides. A solar or photovoltaic cell module (hereafter referred toas a solar cell module) comprises a single solar cell or a planarassembly of interconnected solar cells supported by a load carryingsupporting member. Solar cell modules are typically encapsulated toprotect the cell from the environment. The supporting member of thesolar cell module may be a top layer or superstrate which is transparentto sunlight i.e. positioned between the solar cells and a light source.Alternatively, the supporting member may be a back layer or substratewhich is positioned behind the solar cells. Often solar cell modulescomprise both a superstrate and a substrate. Typically a series of solarcell modules are interconnected to form a solar array which functions asa single electricity producing unit wherein the cells and modules areinterconnected in such a way as to generate a suitable voltage in orderto power a piece of equipment or supply a battery for storage etc.

In general, solar cell modules are made by electrically interconnectingindividual solar cells on a superstrate or substrate and laminating theinterconnected cells into an integral solar cell module. In addition tothe support and protection provided by the aforementioned supportingsuperstrate and/or substrate the light-impinging surfaces of the cellsare also generally protected from the environment (e.g. wind, rain,snow, dust and the like, by being covered with one or more encapsulantor barrier coating materials (Hereafter referred to as“encapsulant(s)”).

Usually wafer based solar cell modules are designed using a superstratewhich is transparent to sunlight fabricated from a material, usually incombination with a substrate and having one or more layers ofencapsulant as a cell adhesive for adhering the cells to the superstrateand when present to the substrate. Hence, light passes through thetransparent superstrate and adhesive before reaching the semi-conductingwafer. The superstrate, typically a rigid panel, serves to protect oneside of the solar cell from potentially harmful environmental conditionsand the other side is protected by the combination of several layers ofencapsulants and a substrate.

A wide variety of materials have been proposed for use as solar cellmodule encapsulants. Common examples include films of ethylene-vinylacetate copolymer (EVA), Tedlar® from E.I. Dupont de Nemours & Co ofWilmington Del. and UV curable urethanes. The encapsulants are generallysupplied in the form of films and are laminated to the cells, andsuperstrate and/or substrate. Prior art examples include the laminationof solar cells using adhesives as exemplified in U.S. Pat. No. 4,331,494and the application of an acrylic polymer and a weather resistant layeras described in U.S. Pat. No. 4,374,955. Solar cell modules have alsobeen prepared by casting and curing acrylic prepolymers onto the solarcells as described in U.S. Pat. No. 4,549,033.

EP 0406814 and U.S. Pat. No. 6,320,116 both describe encapsulationsystems for solar cell or photovoltaic systems. Kondo et al. (SolarEnergy Materials and Solar Cells 49 (1997) pages 127 to 133) describethe use of a thermosetting organic liquid resin as a means ofencapsulating amorphous silicon photovoltaic modules but do not clearlyidentify the resin used.

Typically in the prior art the encapsulants used are filmic andtherefore the layers of encapsulant have to be laminated under heat andvacuum conditions which cause them to melt, bond to adjacent surfaces,and literally “encapsulate” the solar cells.

Currently existing methods for solar cell module encapsulation areusually carried out in a batch mode because of the lamination step whichmakes the entire process slow resulting in the fact that the overallcost of encapsulating the modules is high. In many instances, severallayers of encapsulant may be applied using either the same or differentencapsulant materials for different layers. An example of a prior artmodule is shown in FIG. 1 herein. For example a module may comprising asuperstrate supporting a plurality of solar cells with a first layer ofencapsulant which is transparent to sunlight, utilised as an adhesive,to adhere the superstrate to a series of interconnected solar cells. Asecond or rear layer of encapsulant may then be applied onto the firstlayer of encapsulant and interconnected solar cells. The second layer ofencapsulant may be an additional layer of the same material as used forthe first encapsulant, e.g. ethyl vinyl acetate (EVA) and/or may betransparent or any suitable colour. The substrate is present in the formof a rigid or, a stiff backskin to provide protection to the rearsurface of the module. A wide variety of materials have been proposedfor the substrate, which does not necessarily need to be transparent tolight, these include the same materials as the superstrate e.g. glassbut may also include materials such as organic fluoropolymers such asethylene tetrafluoroethylene (ETPE), Tedlar®, or poly ethyleneterephthalate (PET) alone or coated with silicon and oxygen basedmaterials (SiO_(x)).

Usually a protective seal is provided to cover the edges of the module,and a perimeter frame made of aluminium or a plastic material isprovided to cover the seal. The frame protects the edges of the modulewhen the front cover is made of a fragile material such as glass. Hence,subsequent to lamination and application of the protective seal, themodule is mounted in the frame. Frames suitable for use in combinationwith solar cell modules comprise mounting holes which are provided toenable easy mounting of the resulting framed module to a suitable objectin the field. Typically the mounting process will be accomplished usingany appropriate mounting systems e.g. by way of screws, bolts, nuts andthe like.

Currently one method used to decrease solar cell module manufacturingcosts involves the replacement of the metal, typically aluminium solarcell module frame with a polymeric material for both the substrate andthe edging. For amorphous thin film silicon solar cell modules,polymeric frames made from moulded thermoplastic materials such aspolyurethane are commonly used. These may be prepared by reactioninjection moulding polyurethane to form a frame around an amorphoussilicon cell module. Reaction injection moulding may be done in situ(i.e., on the module), this generally leads to a significant costsaving. However, this moulding process shows several disadvantages. Forexample, this process includes the use of a chemical precursor (e.g.,isocyanate) which poses environmental hazards. This process alsorequires a mould, further adding to the overall manufacturing cost. Themodules made by this process tend to be smaller because of the highercost of the mould and the limited strength of the resulting polymericframe. In this configuration, the encapsulant is still based on severallayers of laminated thermoplastics such as EVA and a fluoropolymer suchas ETFE copolymer. The only cost saving is derived from the costreduction of the frame but potentially renders the resulting solar cellmodule more brittle.

Another problem with solar cell modules currently used in the industryis the fact that thermoplastic laminates are well known to have pooradhesive properties relative to glass. This problem whilst not alwaysinitially evident often leads to gradual delamination of a thermoplasticlayer from glass surfaces in a solar cell over periods of prolongedweathering. The delamination process results in several negative effectson cell efficiency; such as it causes water accumulation in theencapsulant ultimately resulting in cell corrosion. These laminates alsohave a low UV resistance and as such discolour, generally turning yellowor brown over the lifetime of a solar cell, leading to anon-aesthetically pleasing module. Classically, a substantial amount ofadhesive may often be required to reduce delamination effects and UVscreens need to be incorporated in the module to decrease long-termdiscolouration.

For wafer type solar modules e.g. crystalline silicon wafer modules, oneof the main problems is the cost of the materials used; for example, thesubstrate material is generally expensive. There are two widely usedsubstrate materials, both of which tend to be expensive: EVA laminateand Tedlar®, referred to above, a polyvinyl fluoride (PVF) and the otherwidely used substrate material is glass in glass/cell/glassconfiguration.

It is also known that the cost of the encapsulant and the substratematerials, when required, represent a substantial fraction of theoverall cost of each cell and/or module. There is therefore a long feltneed to reduce the costs of encapsulating solar cells in order to reducethe overall cost of their manufacture. The inventors have identifiedthat the overall cost per solar cell module may be reduced by the use ofone or more liquid silicone encapsulants enabling the utilisation of acontinuous encapsulation process which thereby eliminates several stagesin the current solar cell module manufacturing process. The fact thatthe laminate encapsulants are replaced by a liquid encapsulant whichhardens under infrared radiation or thermal cure reduces or eliminatesthe handling of laminate sheets and avoids the need for laminators, thatincrease both encapsulation batch time and cost. The present inventionfurthermore avoids the problems caused by the production of waste fromlamination processes, and the resulting associated materials cost.

In accordance with a first aspect of the present invention there isprovided a solar cell module comprising:—

-   -   i) a rigid or flexible superstrate and/or substrate;    -   ii) one or more solar cells, and    -   iii) a cured liquid silicone encapsulant selected from the group        of a hydrosilylation cure reaction product, a peroxide cure        reaction product and a UV cure reaction product.

In the case where both a superstrate and substrate are present it ispreferred that the solar cells have all their exposed surfaces disposedon either said superstrate or substrate.

The solar cell may be either a wafer or a thin film based and may bemade from any suitable semi-conductor material such as crystalline orpolycrystalline silicon or thin film silicon, e.g. amorphous, semicrystalline silicon, gallium arsenide, copper indium diselenide, cadmiumtelluride, copper indium gallium diselenide, mixtures including any oneor more of the latter and the like. In the case of wafer based solarcells, preferably the wafer is polycrystalline or crystalline silicon.In the case of thin film solar cells, the thin film is preferably madefrom amorphous silicon (aSi), cadmium telluride or copper indium galliumdiselenide. The solar cell may be any suitable type solar cell includingsimple wafer and thin layer solar cells but also split-spectrum cellsand the like. The module may be any suitable type of solar cell moduleincluding concentrators etc.

Preferably, in respect of wafer based solar cell modules in accordancewith the present invention the rigid or flexible superstrate and/orsubstrate comprise a rigid superstrate which is transparent to light.

Preferably, in the case of thin film solar cell modules, the rigid orflexible superstrate and/or substrate comprises a rigid or flexiblesubstrate, such as for example glass or a flexible metal sheet.

The liquid silicone encapsulant in accordance with the inventionpreferably comprises:

-   -   Component (A) 100 parts by weight of a liquid        diorganopolysiloxane having at least two Si-alkenyl groups per        molecule and a viscosity at 25° C. of from 100 to 15,000 nPa·s;    -   Component (B) 20 to 50 parts by weight of a silicone resin        containing at least two alkenyl groups;    -   Component (C) a cross-linking agent in the form of a        polyorganosiloxane having at least two silicon-bonded hydrogen        atoms per molecule, in an amount such that the ratio of the        number of moles of silicon-bonded hydrogen to the total number        of moles of silicon-bonded alkenyl groups is from 0.1:1 to 5:1;    -   Component (D) a hydrosilylation catalyst selected from platinum,        rhodium, iridium, palladium or ruthenium based catalysts, but        which is preferably a platinum based catalyst wherein the amount        of platinum metal in said platinum-based catalyst is from 0.01        to 500 parts by weight per 1,000,000 parts by weight of        component (A).

The proportions of components (A), (B), (C) and (D) may comprise anysuitable amounts. The final viscosity of the resulting uncuredcomposition may be, but is not essentially, able to self-level within ashort period of time after having been dispensed. The preferredviscosity of the final composition is preferably from 100 to 10 000mPa·s measured at 25° C., more preferably from 100 to 5000 mPa·s

Component (A) is preferably a liquid diorganopolysiloxane, representedby the following average unit formula:R_(a)SiO_((4-a)/2)Wherein each R is the same or different and is a monovalent hydrocarbongroup, for example a linear or branched alkyl group such as methyl,ethyl, propyl, isopropyl t-butyl, and pentyl; an alkenyl group such asvinyl, allyl, or hexenyl; and an aryl group such as phenyl. “a” is anumber with an average value between 1.8 and 2.3. Preferably, component(A) has a viscosity at 25° C. of from 100 to 10,000 mPa·s, a molecularstructure which is substantially linear although may be partiallybranched and a relatively low molecular weight of from 10000 to 50000,more preferably from 15000 to 30000. Preferably, component (A) comprisesalkenyl terminal groups.

Examples of component (A) include

a dimethylvinylsiloxy-terminated dimethylpolysiloxane,

a dimethylvinylsiloxy-terminated copolymer of methylvinylsiloxane anddimethylsiloxane,

a dimethylvinylsiloxy-terminated copolymer of methylphenylsiloxane anddimethylsiloxane,

a dimethylvinylsiloxy-terminated copolymer of methylphenylsiloxane,methylvinylsiloxane, and dimethylsiloxane,

a dimethylvinylsiloxy-terminated copolymer of diphenylsiloxane anddimethylsiloxane,

a dimethylvinylsiloxy-terminated copolymer of diphenylsiloxane,methylvinylsiloxane, and dimethylsiloxane, or any suitable combinationof the above

Component (3) is a Silicone resin containing at least two alkenyl groupscomprising SiO_(4/2) units (also known as Q units) and units selectedfrom R′SiO_(3/2) (also known as T units), R′₂SiO_(2/2), and R′₃SiO_(1/2)units, where each R′ may be the same or different and is R or a hydrogenatom. It is preferred to disperse component (B) in a suitable amount ofcomponent (A) or a solvent to ensure ease of mixing with bulk ofcomponent (A). Any suitable solvents may be used such as for examplearomatic solvents such as toluene and xylene, ketones such as methylisobutyl ketone, alcohols such as isopropanol and non-aromatic cyclicsolvents such as hexane. Typically, when a solvent is used, xylene ispreferred.

Component (C) is a cross-linking agent in the form of apolyorganosiloxane having at least two silicon-bonded hydrogen atoms permolecule and has the following average unit formula:R^(i) _(b)SiO_((4-b)/2)where each R^(i) may be the same or different and is hydrogen, an alkylgroup such as methyl, ethyl, propyl, and isopropyl or an aryl group suchas phenyl and tolyl. Component (C) may have a linear, partially branchedlinear, cyclic, or a net-like structure.

Examples of the aforementioned organopolysiloxane include one or more ofthe following:—

a trimethylsiloxy-terminated polymethylhydrogensiloxane,

a trimethylsiloxy-terminated copolymer of methylhydrogensiloxane anddimethylsiloxane,

a dimethylhydrogensiloxy-terminated copolymer of methylhydrogensiloxaneand dimethylsiloxane,

a cyclic copolymer of methylhydrogensiloxane and dimethylsiloxane,

an organopolysiloxane composed of siloxane units expressed by theformula (CH₃)₃SiO_(1/2), siloxane units expressed by the formula(CH₃)₂HSiO_(1/2), and siloxane units expressed by the formula SiO_(4/2),

an organopolysiloxane composed of siloxane units expressed by theformula (CH₃)₂HSiO_(1/2), siloxane units expressed by the formulaCH₃SiO_(3/2),

an organopolysiloxane composed of siloxane units expressed by theformula (CH₃)₂HSiO_(1/2), siloxane units expressed by the formula(CH₃)₂SiO_(1/2), and siloxane units expressed by the formulaCH₃SiO_(3/2),

a dimethylhydrogensiloxy-terminated polydimethylsiloxane,

a dimethylhydrogensiloxy-terminated copolymer of methylphenylsiloxaneand dimethylsiloxane, and

a dimethylhydrogensiloxy-terminated copolymer of a methyl(3,3,3-trifluoropropyl) siloxane and dimethylsiloxane.

Preferably, the viscosity of the cross-linking agent (C) at 25° C. is ina range of from 2 to 100,000 mPa·s. It is recommended that component (C)be added in an amount such that the mole ratio of silicon-bondedhydrogen atoms in the cross-linking agent (C) to the mole number ofalkenyl groups in component (A) is in the range of from 0.1:1 to 5:1,more preferably it is in the range of from 0.8:1 to 4:1. If the aboveratio is lower than 0.1:1, the density of cross-linking will be too lowand it will be difficult to obtain a rubber-like elastomer. A ratiohaving an excess of Si—H groups (i.e. >1:1) is preferred to enhanceadhesion between the superstrate/substrate e.g. glass and theencapsulant.

Component (D) is a hydrosilylation (addition cure) catalyst may compriseany suitable platinum, rhodium, iridium, palladium or ruthenium basedcatalyst. However preferably component (D) is a platinum based catalyst.The platinum-based catalyst may be any suitable platinum catalyst suchas for example a fine platinum powder, platinum black, chloroplatinicacid, an alcoholic solution of chloroplatinic acid, an olefin complex ofchloroplatinic acid, a complex of chloroplatinic acid andalkenylsiloxane, or a thermoplastic resin that contain theaforementioned platinum catalyst. The platinum catalyst is used in anamount such that the content of metallic platinum atoms constitutes from0.1 to 500 parts by weight per 1,000,000 parts by weight of component(A). A hydrosilylation or addition cure reaction is the reaction betweenan Si—H group (typically provided as a cross-linker) and an Si-alkenylgroup, typically a vinyl group, to form an alkylene group betweenadjacent silicon atoms (═Si—CH₂—CH₂—Si═).

The composition may also comprise one or more curing inhibitors in orderto improve handling conditions and storage properties of thecomposition, for example acetylene-type compounds, such as2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol,1-ethynyl-1-cyclohexanol, 1,5-hexadiene, 1,6-heptadiene;3,5-dimethyl-1-hexen-1-yne; 3-ethyl-3-buten-1-yne and/or3-phenyl-3-buten-1-yne; an alkenylsiloxane oligomer such as1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, or 1,3-divinyl-1,3-diphenyldimethyldisiloxane; asilicon compound containing an ethynyl group such as methyltris(3-methyl-1-butyn-3-oxy) silane; a nitrogen-containing compound such astributylamine, tetramethylethylenediamine, benzotriazole; a similarphosphorus-containing compound such as triphenylphosphine; as well assulphur-containing compounds, hydroperoxy compounds, or maleic-acidderivatives.

The aforementioned curing inhibitors are used in an amount of from 0 to3 parts by weight, normally from 0.001 to 3 parts by weight, andpreferably from 0.01 to 1 part by weight per 100 parts by weight ofcomponent (A). Most preferable among the curing inhibitors are theaforementioned acetylene-type compounds, which demonstrate the bestbalance between storage characteristics and speed of curing when theyare used in a combination with aforementioned component (D).

Where required one or more adhesion promoters may also be used toenhance the adhesion of the encapsulant to a superstrate and/orsubstrate surface. Any suitable adhesion promoter may be utilised.Examples include

vinyltriethoxysilane,

acrylopropyltrimethoxysilane,

alkylacrylopropyltrimethoxysilane

Allyltriethoxysilane,

glycidopropyltrimethoxysilane,

allylglycidylether

hydroxydialkyl silyl terminated methylvinylsiloxane-dimethylsiloxanecopolymer, reaction product of hydroxydialkyl silyl terminatedmethylvinylsiloxane-dimethylsiloxane copolymer withglycidopropyltrimethoxysilane; and,

bis-triethoxysilyl ethylene glycol (reaction product of triethoxysilanewith ethylene glycol).

Preferred adhesion promoters are

-   -   i) hydroxydialkyl silyl terminated        methylvinylsiloxane-dimethylsiloxane copolymer,    -   ii) reaction product of hydroxydialkyl silyl terminated        methylvinylsiloxane-dimethylsiloxane copolymer with        glycidopropyltrimethoxysilane; and    -   iii) bis-triethoxysilyl ethylene glycol    -   iv) a 0.5:1 to 1:2, preferably about 1:1, mixture of (i) and a        methacrylopropyltrimethoxysilane

Anti-soiling additives may be utilised, where required to preventsoiling when the solar cells are in use, particularly preferred arefluoroalkene or a fluorosilicone additives that has a viscosity of 10000mPa·s such as:—fluorinated silsesquixoanes, e.g. dimethylhydrogensiloxyterminated trifluoropropyl silsesquioxane, hydroxy-terminatedtrifluoropropylmethyl siloxane, hydroxy-terminatedtrifluoropropylmethylsilyl methylvinylsilyl siloxane,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyltriethoxysilane,hydroxy-terminated methylvinyl, trifluoropropylsilaxane, anddimethylhydrogensiloxy-terminated dimethyl trifluoropropylmethylsiloxane

Preferably, the anti-soiling additive is present in an amount of from 0to 5 parts by weight, more preferably 0 to 2 parts by weight and mostpreferably 0 to 1.5 parts by weight. Preferably when the encapsulant isused both in the absence of the adhesive layer referred to below theanti-soiling additive is included in the encapsulant composition as wellas when used in combination with the adhesive layer.

Other additives that enhance the physical properties may be utilised inthe composition. One particular example is the inclusion of a fireretardant. Any suitable fire retardant or mixture of fire retardants maybe used providing they do not negatively affecting the other physicalproperties of the encapsulant composition. Examples include aluminapowder, or wollastonite as described in WO 00/46817. The latter may beused alone or in combination with other fire retardants or a pigmentsuch as titanium dioxide. In cases where the encapsulant need not betransparent to light, it may comprise a pigment.

In one aspect of the present invention the solar cell module comprisesthin film solar cells. Preferably, a solar cell module comprising thinfilm solar cells requires a single layer of encapsulant. In the casewhere a single layer of encapsulant is utilised the silicone encapsulantis designed to be hard and scratch resistant and thereby is designed tofunction as both an adhesive/top coat and avoids the need for anexpensive substrate of the type generally utilised in the prior art.Preferably, solar cell modules comprising a single layer of encapsulantincorporate the aforementioned anti-soiling additive.

In the case when a single layer of encapsulant is utilised it ispreferred that component (C) of the formulation has an excess of Si—Hgroups, i.e. the ratio of the number of moles of silicon-bonded hydrogento the total number of moles of silicon-bonded alkenyl groups ispreferably 0.8:1 to 5:1, more preferably >1:1 and most preferably from1:1 to 4:1.

Hence in the case of a solar cell module with a single layer ofencapsulant in accordance with the present invention, Component (A)preferably is a high molecular weight polymer, component (B) is presentin an amount of from 30 to 50 parts by weight of a silicone resincontaining at least two alkenyl groups and Component (C) is across-linking agent in the form of a polyorganosiloxane having at leasttwo silicon-bonded hydrogen atoms per molecule, in an amount such thatthe ratio of the number of moles of silicon-bonded hydrogen to the totalnumber of moles of silicon-bonded alkenyl groups in component is from0.8:1 to 5:1 and more preferably from 1:1 to 4:1. Furthermore, thecomposition comprises an anti-soiling additive.

Any suitable process may be used to prepare the uncured liquid siliconeencapsulant; for example, component (B) may be premixed with component(A) and component (C) and then co-cross-linked in the presence of a lowlevel of platinum catalyst to form a tough polymer network. A smallamount of a catalyst inhibitor such as ethylhexynol may be added toprolong the bath time of the encapsulant. When heated above 90° C., themixture initially forms a non-transparent two-phase system due to thepresence of the anti-soiling additive and then becomes highlytransparent. To ensure the long lasting bonding of the encapsulant toall adjacent surfaces, a small amount of adhesion promoter is preferablyuse. It is believed that the adhesion promoter migrates to the interfaceof the topcoat and reacts irreversibly with adjacent surfaces. Thisstrong adhesion allows the module to function in wide range oftemperatures from ambient temperature to extremes without delaminating.

The single layer encapsulant is designed to have a required abrasionresistance to prevent further damage that may occur duringtransportation or in field usage. It is tough enough to serve also asthe substrate protecting the cell.

The combination of encapsulant and topcoat is designed to replacemultiple layers and material chemistry of the classical configuration(EVA and fluoropolymer laminate) by two layers based on one corechemistry. The topcoat preferably covers the entire cell interconnects;it functions as an outer layer i.e. as an environmentally protectinglayer.

Component (B) of the composition as hereinbefore described is providedbecause silicone resins of this type impart outstanding UV resistance tothe encapsulant and therefore there is no need for the inclusion of oneor more UV screen additives which in the case of most prior artformulations was typically essential. The cured liquid siliconeencapsulant of the type described in the present invention exhibits longterm UV & visual light transmission thereby allowing the maximum amountof light to reach solar cells.

Whilst the UV resistance capabilities of silicone based compositions iswell known the commercial exploitation of such formulations have beenlimited by high total cost and a lack of suitable process to dispense aliquid encapsulation.

In the case of thin film solar cell modules the inventors have foundthat the encapsulant as hereinbefore described is adequate to replacethe often several layers of encapsulant and avoids the need for asubstrate. The encapsulant is located between e.g. a glass platesuperstrate and the solar cell and its primary function is to protectthe solar cell against mechanical stress arising from temperaturechanges, and to adhere the solar cell to the superstrate.

However, particularly in the case of wafer type solar cell modules ithas been identified that in some instances an optional adhesive layercomprising a further liquid silicone encapsulant may be utilised for theadhesion of the wafer type solar cells onto the load bearing support,typically a superstrate.

The liquid silicone encapsulant utilised as the intermediate adhesivelayer (henceforth referred to as the adhesive) is preferablysubstantially the same basic formulation as the single layer encapsulantdescribed to above and preferably comprises:

-   -   Component (Ai) 100 parts by weight of a liquid        diorganopolysiloxane having at least two Si-alkenyl groups per        molecule and a viscosity at 25° C. of from 100 to 10,000 mPa·s;    -   Component (Bi) 20 to 40 parts by weight of a silicone resin        containing at least two alkenyl groups;    -   Component (Ci) a cross-linking agent in the form of a        polyorganosiloxane having at least two silicon-bonded hydrogen        atoms per molecule, in an amount such that the ratio of the        number of moles of silicon-bonded hydrogen to the total number        of moles of silicon-bonded alkenyl groups is from 0.1:1 to 1:1;    -   Component (Di) a hydrosilylation catalyst selected from        platinum, rhodium, iridium, palladium or ruthenium based        catalysts, but which is preferably a platinum based catalyst        wherein the amount of platinum metal in said platinum-based        catalyst is from 0.01 to 500 parts by weight per 1,000,000 parts        by weight of component (Ai).

The proportions of components (Ai), (Bi), (Ci) and (Di) may comprise anysuitable amounts. The final viscosity of the resulting uncuredcomposition may be, but is not essentially, able to self-level within ashort period of time after having been dispensed. The preferredviscosity of the final composition is preferably from 100 to 2000 mPa·smeasured at 25° C., more preferably from 500 to 1000 mPa·s.

Preferably, the viscosity of component (Ai) of the adhesive is lowerthan the viscosity of component (A) of the aforementioned encapsulant.Preferably when both encapsulant and adhesive are utilised, theencapsulant comprises a resin fraction of between 20% to 90% by weight,preferably between 25% to 70% and more preferably between 30-60% and theadhesive comprises a resin fraction of from 20-30% by weight.

The adhesive may also comprise any one or more of the optional additivesdescribed with respect to the encapsulant formulation. Preferably theadhesive layer comprises a suitable adhesion promoter, most preferablyone of the adhesion promoters listed above with respect to theencapsulant composition.

The adhesive composition may be cured by any suitable process, forexample component (Bi) may be premixed with components (Ai) and (Ci) andthen co-cross-linked in the presence of platinum catalyst to form atough network. Preferably, a small amount of a catalyst inhibitor, suchas for example ethylhexynol, is added to allow a prolonged bath time ofthe material. To ensure a long lasting bonding interaction between theencapsulant and all adjacent surfaces, a small amount of adhesionpromoter, typically an alkoxysilane, is added and the ratio of Si—Hbonds to Si-alkenyl bonds is lower than 1:1, such as for example 0.6:1.It is believed that the adhesion promoter migrates to the interface ofthe encapsulant and reacts irreversibly with adjacent surfaces. Thisstrong adhesion allows the module to function over a wide range oftemperatures without or substantially without delaminating. The excessof alkenyl groups also helps the bonding/adhesion of the intermediatelayer of adhesive with the encapsulant which is in this case functioningas a topcoat.

Both the encapsulant and, where utilized, the adhesive providehomogeneous and transparent silicone films that maintains a highflexibility due to the presence of the linear or substantially linearpolymers of component (A). The encapsulant, when cured, has a highertear resistance than the adhesive. The anti-soiling additives are addedto the encapsulant, to increase the soil resistance of the material andare used in amounts which will not noticeably negatively affect theabrasion resistance properties thereof. In a composition such as that ofthe encapsulant of the present invention, the anti-soiling additives arebelieved to migrate and spread rapidly at the silicone/air interfacemaking a low surface energy surface but remain chemically bonded to thesilicone matrix. The soil accumulation on the outwardly facing side (atthe interface with the environment) of the encapsulant is inverselyproportional to the surface energy, which is related to the level ofanti-soiling additives on the surface.

In use when anti-soiling additives are included in the encapsulantcomposition; first, a surface phase separation occurs; the anti-soilingadditive migrates to the surface and then reacts with the cross-linkergiving a fluorine-covered surface. The platinum concentration at thesurface increases due to inhibitor evaporation, leading to a gradientcure rate of the film from the surface to the bulk. The overall resultproviding a much harder surface and smoother bulk material that allowsstress relaxation interface between the glass and the wafer.

In one aspect, the invention features a transparent encapsulant formedof a silicone composition that provides good adhesive properties to thefront glass and to the solar cells. The encapsulant plays the role of apotting material, showing a good adhesion to the interconnected solarcells, to the connecting wires and to the superstrate e.g. a glass plate(wafer modules). The adhesion of the encapsulant to solar cells requiresa good wetting of the cell and on an occasion, it was found desirable toprovide such wetting by means of the adhesive, which preferably has alower viscosity than the encapsulant.

In the case of peroxide cure encapsulant product any suitable liquidsilicone composition may be used. Typically peroxide catalysts are usedfor free-radical based reactions between siloxanes comprising:—

≡Si—CH₃ groups and other ≡Si—CH₃ groups; or

≡Si—CH₃ groups and ≡Si-alkenyl groups (typically vinyl); or

≡Si-alkenyl groups and ≡Si-alkenyl groups. For peroxide cure componentsA and B above would preferably be retained with a suitable peroxidecatalyst and any or all of the additives described above (with theexception of the cure inhibitors which are specific to hydrosilylationtype catalysis) may be utilised. Suitable peroxide catalysts may includebut are not restricted to 2,4-dichlorobenzoyl peroxide, benzoylperoxide, dicumyl peroxide, tert-butyl perbenzoate.In the case of UV cure systems any suitable liquid silicone polymer maybe utilised together where appropriate with a UV photoinitiator. For UVcure systems any or all of the additives described above (with theexception of the cure inhibitors which are specific to hydrosilylationtype catalysis) may be utilisedAny other suitable cure system for curing organopolysiloxanes may beutilised providing the uncured organopolysiloxane composition used issuitable for application in accordance with any one of the processesdescribed below.

The inventors have also found a new way of passivating the surface of asolar cell and/or photovoltaic cell which may be encapsulated by anysystem i.e. using the composition as described in the present inventionor the prior art processes and lamination techniques. The coating of thecell surface with a trialkoxysilane results in a primer or passivatinglayer which has good adhesion to the cell surface and typically to theencapsulant used. It will passivate the surface and thereby increase thewetting of the cell(s) in order to reduce or avoid problems with bubbleformation between the cell and the encapsulant and/or adhesive. It willalso protect the cell after encapsulation from water ingress andcorrosion. The chosen silane may be applied as a precoating onto thesolar cell(s) or may be added in a suitable concentration in theencapsulant composition. The pre-coating may comprise the silane aloneor a solution of the silane in a solvent such as an alcohol, the latterof which is allowed to evaporate after application. Typically, the layerof the passivation coating might be as small as 2 μm thick. Mostpreferably the passivation layer is provided on wafer type solar cells.Preferably the silane has the formula:—(R¹O)₃SiR²wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms, R² isselected from the group of an alkoxy group comprising 1 to 6 carbonatoms, an alkyl group comprising 1 to 6 carbon atoms an alkenyl groupcomprising 1 to 6 carbon atoms, an acrylic group or an alkyl acrylicgroup. Preferably, the trialkoxysilane is for example, atrimethoxysilane or triethoxysilane, most preferablymethacrylopropyltrimethoxysilane.

Advantages of the solar modules encapsulated using the liquid siliconeencapsulant described above include:—

-   -   i) A reduction of the Total cost-in-use of modules i.e. a        reduction in the total cost taking all the parameters including        material, application process, quantity of material per square        meter);    -   ii) Module Durability—modules made using the compositions        described in the present invention are both enhance efficiency        of manufacture and reduce problems of discoloration after ageing        due to UV exposure.    -   iii) Due to the physical properties of the liquid silicone        encapsulant fire resistant properties are significantly improved        over prior art modules.    -   iv) The application of the encapsulant and, where used, the        adhesive by any chosen method using the compositions described        in the present invention, e.g. curtain coating is undertaken at        room temperature (although some heating may be utilised).

In another aspect of the present invention there is provided acontinuous method of encapsulating solar cell modules using the liquidsilicone encapsulant material described above.

The current standard industry process generally utilizes an EVA (ethylvinyl acetate) thermoplastic encapsulant and a laminatable backingmaterial such polyester/Tedlar® and the cell or array of cells/module isprepared using a lamination technique. Typically, a suitable laminatoris used to laminate the following “sandwich” of layers.

-   -   1) Glass superstrate,    -   2) EVA,    -   3) solar cell series,    -   4) EVA, and    -   5) Substrate in the form of a suitable backing material

The standard process uses the laminator apparatus to melt the layers ofthe “sandwich” at a temperature in the region of 140° C. (actualtemperature used is determined in view of the actual composition beinglaminated) under vacuum for about 20 minutes per module. Afterlamination and the removal of waste material, surplus to requirements,the next step of the batch process is usually the application aprotective seal is provided to cover the edges of the module, followedby the framing of the module in the perimeter frame, typically made ofaluminium or a plastic material and discussed previously. The overalloperation is carried out in a batch mode and is typically slow and verylabour intensive.

In order to simplify the description around the process in accordancewith the present invention the process will be described for both thinfilm and wafer type solar cell modules with respect to the cells beingsupported on a glass supporting superstrate or substrate, but it is tobe understood that the process of the present invention can be utilisedfor any suitable module composition by merely adapting the process tothe needs of the module in question.

In the present invention, in the case of thin film solar cells on aglass substrate or superstrate, a transparent encapsulant layer issprayed, coated or dispensed uniformly on a thin film solar cell moduleby way of any suitable type of dispensing equipment such as for examplecurtain coaters, spray devices, die coaters, dip coaters, extrusioncoaters, knife coaters and screen coaters and the like, but preferablyby means of a curtain coater and the resulting module is then curedthermally or by infrared radiation, a suitable heating or IR radiationsource for example a continuous oven or an in-place heating means suchas an oven or hot plate or the like, preferably a continuous oven. Thespraying, coating or dispensing step may be undertaken at any suitabletemperature but preferably is undertaken at a temperature of from roomtemperature, e.g. about 25° C. to about 75° C., although roomtemperature is preferred.

Typically for thin film solar cell modules the inventors have found thatno additional adhesive is required as the encapsulant bonds sufficientlywell directly with the solar cell and substrate/superstrate. However,for wafer based solar cells, an adhesive layer is required to adhere thesolar cell, (i.e. the wafer) to the superstrate or substrate. Whilstthis may be in the form of a layer of the encapsulant as describedabove, the adhesive described above is preferably used.

The liquid encapsulant and, where used the adhesive are both designed tocure and therefore harden in a well-defined thickness when submitted toinfrared or thermal radiation. The use of encapsulant, and whererequired the adhesive, enables the user to operate a continuous processin which a liquid silicone encapsulant may be applied onto solar cellsby way of any suitable type of dispensing equipment such as for examplecurtain coaters, spray devices die coaters, dip coaters, extrusioncoaters, knife coaters and screen coaters and the like. The pre and postencapsulated modules may be fed continuously using a conveyor for planarand rigid superstrates or substrates such as glass or fed in a roll toroll process for flexible superstrates or substrates such as stainlesssteel foils.

One major advantage of the process in accordance with the presentinvention is that the encapsulant is therefore applied to the cellsurface without or substantially without air bubble entrapment, a majorproblem under current processes because air bubbles are believed toretain moisture in high humidity conditions and in use solar cells canbe subjected to huge temperature variations. The presence of moisture isdetrimental to solar cell modules as it condenses into liquid waterwhich may induce local corrosion of metallic contacts, on solder or onsolar cells and furthermore may cause early delamination of the modules.

In the case of interconnecting wafer type solar cells, the adhesive ashereinbefore described is preferably sprayed, coated or dispenseduniformly onto the back of a superstrate or substrate, e.g. a glassplate by means of curtain coaters, spray devices, die coaters, dipcoaters, extrusion coaters, knife coaters and screen coaters and thelike, preferably a curtain coater. Then the interconnected solar cellsare deposited onto/in to the uncured adhesive. The adhesive is thencured/hardened thermally or by infrared radiation in such a way that theadhesive fixes the interconnected solar cells in a predefined positionon the superstrate/substrate, by a suitable heating or IR radiationsource for example a continuous oven or an in-place heating means suchas an oven or hot plate or the like. Then an amount of encapsulant asdescribed hereinbefore is uniformly applied to totally encapsulate thewhole module by means of curtain coaters, spray devices, die coaters,dip coaters, extrusion coaters, knife coaters and screen coaters and thelike, preferably a curtain coater and the resulting module is thencured/hardened thermally or by infrared radiation using a suitableheating or IR radiation source for example a continuous oven or anin-place heating, preferably a continuous oven.

Alternatively for wafer based solar cell systems a sufficient amount ofencapsulant or if used adhesive is sprayed, coated or dispenseduniformly onto a glass superstrate/substrate and then theinterconnecting solar cells are carefully immersed into a further amountof the same material and subsequently the resulting module is cured andhardened either thermally or by infrared radiation and where required atop-coat of encapsulant is sprayed, coated or dispensed (as describedabove) uniformly onto the cured adhesive and subsequently is cured andhardened either thermally or by infrared radiation as described above.

In one aspect of the present invention, the frame or edge sealingmaterial may be applied to the substrate/superstrate beforeencapsulation and not after completion of the encapsulation process viathe laminating processes of the prior art. This forms a guide for wherethe encapsulant and/or adhesive needs to be applied in liquid form.

Preferably the application of both encapsulant and adhesive may becarried out at about room temperature but some heating may be utilisedup to e.g. a temperature of 75° C., preferably no greater than 50° C. inorder to reduce the viscosity of the encapsulant or adhesive beingapplied on to the module.

Preferably, the electrical leads in a module are treated using either ofthe above suggested methods are protected against coating withencapsulant and/or if used adhesive. The protected leads may be furtherbonded into an electrical junction box on the substrate or back skinmaterial to form an integral seal. The liquid silicone coatings may besealed and inserted into a metal, thermoplastic or elastomeric framewhich also provide additional protection against water ingress at theedge of the panel. However, it was identified that with a siliconeencapsulant in accordance with the present invention such a frame wasnot necessarily required unlike for solar cell modules prepared by theprior art lamination type processes.

One very important aspect when compared to prior art lamination basedprocesses is that the entire process in accordance with this aspect ofthe invention may be automated into an integrated assembly line withprocess control and as such is a significantly less labour intensive.

In a preferred embodiment of the process in accordance with the presentinvention there is provided a continuous process using one or more meansof coating the encapsulant and adhesive (where used) such as curtaincoaters, spray devices and die coaters dip coaters, extrusion coaters,knife coaters and screen coaters and the like, although curtain coatersare preferred followed by an appropriate curing step, typically using athermal or IR oven.

This process may be used for both organic and silicone systems providedthe viscosity of the coatings involved are suitable for use incombination with the means of applying the coating such as a curtaincoater, although the process is preferably used in combination withencapsulant and adhesive formulation of the type described herein.Hence, preferably the viscosity of the uncured composition is no greaterthan 50000 mPa·s and most preferably no greater than 40000 mPa·s.

The preferred means of applying encapsulant and where required adhesiveis by means of a curtain coater. Curtain coating is a process forapplying a thin layer of liquid onto a solid material. Curtain coatingmachines are adapted to disperse liquid at a controlled rate over thewidth of its coating head onto a target (in the case of this applicationsolar cell modules). The resulting wide, thin flow of liquid resembles a“curtain” hence the name “Curtain Coater.” By passing the target (thesolar cell modules) under the curtain of liquid at a predefined constantspeed an even layer of liquid is deposited on the target (the solar cellmodules). The ability of the user to control both the flow rate of theliquid and the speed of the target through the curtain of liquid a veryaccurate thickness of the coat is obtained.

Encapsulant or adhesive is initially retained in a reservoir tank, andwhen required is pumped from the tank, through a filter to coating head.The coating head may be either pressurised or non-pressurised dependingon the viscosity of the coating being used (but in the present inventionwill usually be pressurized due to the viscosity of the encapsulant andadhesive when used. The encapsulant or adhesive flows through a dye inthe coating head to form a ‘curtain’ of liquid under the effects ofgravity. The Solar cell module to be coated is transferred along anin-feed conveyor, through the curtain of material, and onto an out-feedconveyor. Preferably the ‘curtain’ of encapsulant or adhesive is widerthan the solar cell modules being coated so that all excess materialfalls through a gap between the in-feed and out-feed conveyors into acollection trough, and flows back to the feed tank, thereby avoiding anyunnecessary waste.

The feed tank is typically deep and constructed with baffles, so thatthe encapsulant or adhesive must follow a “tortuous” path, thus allowingtime for any entrained air to escape before getting to the pump suction.

A curtain coater is generally used for processes involving much lessviscous liquids and it was imperative for the process of the presentinvention that the curtain coater used did not cause frothing and orbubbling. Several adjustments were required in the stock equipment tohandle liquids of the viscosities of the encapsulant and adhesivedescribed in the present invention. These were mainly directed toreducing the amount entrained air in the system to minimise thelikelihood of the encapsulant and adhesive where used to foam or retainair bubbles. The curtain coater was preferably fitted with high poweredpumps as the standard diaphragm pumps cannot be used since theyintroduce air into the system and would not be practical for applicationof the liquid encapsulant which may have a relatively high viscosity fora liquid of up to e.g. 10.000 mPa·s.

Preferably, the curtain coater has a centre feed system. This is becausewhilst lower viscosity liquid can be fed from any position on the coaterhead, but as the viscosity of the liquids utilised is higher thannormally expected for use with this type of coater resulting in the needfor longer times than normal being required for levelling theencapsulant and/or adhesive in the modules.

Preferably, the curtain coater feeder head utilises surface feed toavoid the entrainment of air. This is because whilst lower viscosityliquids of the type typically applied by curtain coaters are fed in anysubmerged depth position (z dimension) from the bottom to the top of thecoater head tank, normally it is fed in a submerged manner to controlsplashing.

Preferably, the curtain coater has an anti-splash “pan” at the bottom ofthe curtain fall. This is provided in the form of a rolled metal panwhich is provided to contribute to the laminar flow into the dischargeand help prevent entrained air.

Preferably the Feed tanks are preferably both larger (overall capacity)and taller than normal feed tanks used for standard curtain coaters, toallow entrained air bubbles to rise to the surface of the tank accordingto Stokes law, and again help reduce the entrained air.

Preferably the normal operating speed of the curtain coater may belowered as compared to prior art curtain coaters. This is preferablebecause the lower operating speed range of the coater conveying systemin order to allow better speed control of the speed of feeding the glasssuperstrates and/or substrates through the curtain coater, therebyproviding better control curtain thickness.

Preferably, the curtain coater comprises a plurality of several curtainguides to the coater head to control the width of the curtain and/orallow the use of a multiple series of curtains. This provided coatingflexibility and permitted the use of the same coating equipment for thecoating of many different sizes of solar modules and arrays and thelike.

Preferably, the curtain coater comprises a long return pipe andcoalescer to remove gross bubbles from the system.

The curtain coater may also optionally comprise a heating system to heatthe liquid as it approaches the curtain. Heating the encapsulant andadhesive when used to about 50° C., has the advantage of reducing theviscosity and enhances the probability of any microscopic bubblespresent in the composition to be applied to rise to the surface.

Preferably the encapsulant and where used adhesive is de-aired prior tocoating. Any suitable de-airing process may be utilised, e.g. by vacuumbut preferably the curtain coater is provided with a semi-continuousvacuum stripper to de-air liquid before feeding it into or back into thecoater head.

Preferably a multi-axis robot, (preferably six axes) may be integratedinto the system for automating the accurate positioning of the solarcell modules on the in-feed conveyor belt and for accuratelyinserting/placing a solar cell or series of interconnected solar cellsin position on the substrate or superstrate. This is particularlypreferred in the case of wafer based solar cell systems wherepositioning of the cell on the superstrate or substrate is particularlycritical. Any suitable robot may be utilised. The robotic gripper forholding and manipulating the solar cells or solar cell modules (i.e. thedevice attached to the mounting arm of the robot that will manipulatethe solar cells or solar cell modules) may be of any suitable type butis preferably a series of vacuum suction cups adapted to hold the solarcells or solar cell modules in a flat (typically horizontal) plane.

In the case of an interconnected series of solar cells the gripper platepreferably has at least one vacuum cup per cell to avoid any stress onthe tabs over, under, and between the cells. Typically for a singlesolar cell a single vacuum cup is utilised pulling the cell upward tofour Teflon pins that determined an exact position. Typically for eachsolar cell, one or two small vacuum cups are utilized, pulling the solarcell upward to a positioning stops or pins that determine the exactposition of the cell relative to the substrate or superstrate and enableexact placement of the cell on the substrate or superstrate.

The robot may for example pick up these a solar cell or series ofinterconnected solar cells from a fixed position and then place theminto a thin liquid silicone layer on a superstrate or substrate (a glassplate). The glass plate may be edged with a cured sealant dam to holdthe liquid in place. The glass plate may be mounted on top of a specialnear-IR oven that was fabricated to cure the liquid as the cells wereheld in place by the robot. The robot was adapted to manipulate thecells so that the best wetting method could be determined. In general,in the case of a single solar cell one edge of the solar cell was placedinto the liquid and the remainder of the solar cell was lowered at apredetermined speed and angle to allow a meniscus of liquid to graduallyflow over and wet the cell. Preferably the robot comprises a servomotorsuch that the speed of insertion of the solar cell is graduallydecreased as the angle of the cell into the liquid became closer to thehorizontal. In the case of a four cell array being placed edgewise, thatis, with the aligned edge of all four cells forming the turning point,the cells were applied without bubble formation.

Any suitable oven may be utilised for curing applied layers ofencapsulant and adhesive, continuous ovens are particularly preferredfor curing applied layers of encapsulant. The continuous ovens maycomprise short wave IR emitters (wavelength 1.2 to 1.4 μm), medium waveIR emitters (wavelength 1.4 to 2.7 μm) but preferably comprise mediumwave emitters and the temperature in the oven will be optimised for thecoating concerned but will typically be in the region of from about 120to about 200° C. Preferably in the cases when an adhesive layer isutilised the module containing a solar cell or series of interconnectedsolar cells is held in place by means of the robot and cured in situusing any appropriate heating means such as a static oven or hot plateat a temperature of in the region of between 150 and 250° C.

A process for the application of both adhesive and encapsulant may forexample comprise the following steps:

-   -   1) a suitable framing or sealing material is applied to a        cleaned glass substrate or superstrate panel, preferably this        takes place on an XY table onto which the plate had been        previously positioned. The framing material is utilized to        protect the edges of the panel and importantly provides a        moisture barrier, and serves as a dam to contain the liquid        encapsulant and where used adhesive prior to cure.    -   2) The resulting framed glass panel is conveyed through a        continuous oven to fully cure the framing or sealing material.    -   3) The panel with the cured framing material is conveyed through        a means of applying a layer of adhesive (preferably by means of        a curtain coating (although any of the other referred to above        may be utilised) operation). Preferably a layer of 150 to 1000        g/m, more preferably a layer of about 400 μm of adhesive        material is applied in a very even coat.    -   4) If required the multi-axis robot may pick up a solar array        (of interconnected solar cells) using, for example, a vacuum cup        gripper, and then dip coats the solar array into a trialkoxy        silane primer which is adapted to protect the cells against        moisture. This primer also passivates the solar cell surface to        assist in the avoidance of bubble formation during the curing        process of the adhesive.    -   5) In the case where step 4 occurs the silane treated        interconnected series of solar cells is then dried preferably by        use of the robot. The robot then places the primed series of        solar cells onto the framed panel, and into the layer of        adhesive, using for example a slow six axis motion wherein in        such cases a final, very accurate placement of the cells occur        provided by a seventh axis on the gripper. Preferably this        placement is done on an extremely flat “engineered” table that        provides very accurate repeatability of placement. This table        solves the many tolerance issues inherent in the glass and the        solar cells. Preferably, this engineered table has a built-in        heater that cures the adhesive layer within a few minutes and        thus fixes the cells into a permanent position after which the        robot is adapted to release the vacuum and the panel moves to        the next step. However, alternatively the glass/cell/adhesive        combination may be cured in a continuous oven.

The resulting post-cured panel “assembly” is then conveyed through asecond curtain coater where a layer of from 20 μm to 1200 μm, preferablybetween 50 μm to 1000 μm, more preferably between 200 μm to 700 μm evenmore preferably 400 μm to 800 μm and most preferably 400 μm to 700 μm ofthe encapsulant is applied in a very even coat.

The module having had the encapsulant applied is then conveyed through asuitable continuous (e.g. convective/IR) oven where the encapsulantcures into a smooth tough backing material.

The final framed panel is then conveyed into a staging area which issimilar and may even be the same as for existing systems where theelectrical junction box is attached, and the panel is either packaged orprogresses, where required, to a framing step. The framing material usedis a thermoplastic or other suitable damping material also helps in thisstep because the cured framing material is bolted into an aluminiumprofile without any “squeeze out”. This squeeze out of excess frameprotection material is a problem with the double sided tape or sealantthat is currently used in the industry, since it requires trimming andglass cleaning.

The entire process in accordance with the present invention is anautomated assembly line, or continuous unit-operation manufacturing,using electronic process control such as PLC. There are sensors,conveyors, limit switches and buffering areas (for any mis-matches inrates of particular unit-operations). Preferably, the continuous processof the present invention provides one linear meter of panel per minutewhich is a significant improvement over the current production speed.

The invention will be more clearly understood from the followingdescription of some embodiments thereof given by way of example onlywith reference to the accompanying drawings, in which

DRAWINGS

FIG. 1 illustrates a conventional solar cell module in a frame;

FIG. 2: illustrates a further conventional thin film solar cell;

FIG. 3: illustrates a wafer type solar module;

FIG. 4: illustrates a wafer type solar module without a classicalperimeter aluminum frame;

FIG. 5: illustrates a preferred solar module encapsulation process forwafer type solar modules; and

FIG. 6: illustrates a continuous encapsulation process of making a wafertype solar cell module.

FIGS. 1 and 2 illustrate conventional wafer type solar cell modules. InFIG. 1 there is provided a wafer type solar cell module 1 with a Tedlar®substrate or backskin 2. The module also consists of a front glasssuperstrate 3, interconnected solar cells 4 sandwiched between two EVAsheets 5,6. A further interconnecting layer 9 comprising any suitablematerial may be provided between EVA sheets 5,6, however, typicallyinterconnecting layer 9 comprises a mixture of materials from the twoEVA sheets 5,6. Typically Tedlar® substrate or backskin 2 isprelaminated to EVA sheet 6 before lamination in the solar cell module.The module 1 is edged with rubber seal 7 that makes a junction to analuminium frame 8. In FIG. 2 there is shown a conventional thin filmtype solar cell module 10 with a TEFZEL superstrate 11, a thin filmsilicon solar cell 12 on stainless steel substrate 13, sandwichedbetween two EVA sheets 14, 15. A further interconnecting layer 16,comprising a suitable material may be provided between EVA sheets 14 and15, however, typically interconnecting layer 16 comprises a mixture ofmaterials from the two EVA sheets 14,15. In both cases, theencapsulation is obtained by means of lamination techniques such thatthe different layers shown are laminated with their neighbours. Thisprocess can be labourious and must be carried out in a batch typeprocess.

FIG. 3: illustrates a wafer type solar module 20 with a perimeteraluminium frame 21, a front glass superstrate 22, a junction box 23 andinterconnected solar cells 24 encapsulated in accordance with a curedsilicone encapsulant 25 in accordance with the present invention. Inthis example a substrate 26 is shown but whilst this may be utilisedtypically the encapsulant of the present invention to encapsulate asolar cell module should suffice without the need for any such backskinunless there is a specific reason due to the application involved.

FIG. 4: illustrates a wafer module 30 without a classical perimeteraluminium frame of the type indicated as 21 in FIG. 3. It comprises afront glass superstrate 31 and a junction box 32. Interconnected wafertype solar cells 34 are provided in predetermined positions relative toeach other 34 and the superstrate 31 in a layer of silicone adhesive 33.A top-coat of silicone encapsulant 35 is provided as a hard surface toprotect the wafers 34 from the environment in order to enhance thelifetime of the solar module as a means of generating electricity fromsunlight. Electrical leads linking adjacent wafers 34 are coated in sucha way that they may be further bonded into the back skin material or asin this case the silicone encapsulant to form an integral seal.

FIG. 5: is provided to illustrate an encapsulated thin film type solarmodule in accordance with the present invention. There is provided asubstrate or support 37 onto which has been coated a thin film ofsuitable semi-conducting material 39. The thin film is encapsulatedusing a layer of the silicone encapsulant 38 in accordance with thepresent invention. Typically, the thin film will have been appliedpreviously onto substrate 37 by, for example, chemical vapour depositionor sputtering techniques.

FIG. 6 is intended to assist the reader to appreciate the continuousencapsulation process described in the present invention. The processdescribed relates to the encapsulation of a wafer type solar cellmodules requiring both an adhesive layer and an encapsulant layer tofully encapsulate the module. There are provided three conveyor belts50, 51, 52 for transporting solar cell modules 53 a, 53 b, 53 c, 53 d,53 e through the stages of the encapsulation process. There is alsoprovided a first curtain coater 54 for application of silicone adhesive.A collector 55 is positioned under curtain coater 54 to collect unusedsilicone adhesive. A pump (not shown) is provided to return said unusedsilicone adhesive from collector 55 to a storage tank 56 which suppliessilicone adhesive to curtain coater 54. A six-axis robot 57 is utilisedfor the accurate placement of solar cells or groups of interconnectedsolar cells into or onto a layer of uncured silicone adhesive on module53 b before curing of the silicone adhesive. Any suitable number ofelectrically interconnected solar cells may be utilised. A first oven 58is provided as the means of curing the adhesive layer. A second curtaincoater 59 is provided for the application of silicone encapsulant ontothe cured adhesive layer of module 53 d. A collector 60 is provided tocollect unused silicone encapsulant which is returned to a storage tank61 or direct to curtain coater 59 for reuse. A second oven 62 isprovided to cure the encapsulant layer onto the adhesive layer.

In use a Solar cell module is initially placed on conveyor belt 50 andis transported to the end of conveyor 50 and through a curtain of liquidsilicone adhesive supplied by curtain coater 54, as indicated by module53 a. Subsequent to application of the liquid silicone adhesive themodule is transported along conveyor 51 to a predetermined position (asidentified by module 53 b) where a solar cell or series ofinterconnected solar cells are accurately positioned at a predeterminedposition in or on the uncured liquid adhesive layer by robot 57.Subsequent to the positioning of the cell(s), the module continues to betransported along conveyor 51 through a continuous oven 58 (it will beappreciated that the continuous oven is only one of the alternativemeans of curing the adhesive layer). Preferably when used the oven is ofan IR type.

After the adhesive layer has been cured in oven 58 thereby rigidlypositioning the cell(s) in the module, a module is transported to theend of conveyor 51 to the second curtain coater 59 where a layer ofliquid silicone encapsulant is applied (53 d). The module is thentransported through oven 62 on conveyor 52 in order to cure theencapsulant layer on top of the adhesive layer (53 e), after which thefully encapsulated solar cell may be removed from the conveyor andstored for future use.

EXAMPLES Example 1 Preparation of Silicone Composition of this Invention

35.42 g of α,ω-dimethylvinylsiloxy terminated polydimethylsiloxanehaving a molecular weight of 62000 g/mole and vinyl content of 0.15%; 7g of poly(dimethyl siloxane-co-methylhydrogensiloxane) containing 1.45%of hydrogen units; 47.22 g of p-xylene solution of dimethylvinylated MQresin (63% resin in Xylene) were intimately mixed and the p-xylenestripped out under reduced pressure. After solvent removal, 0.825 g ofdimethylhydrogen siloxy terminated trifluoropropyl silsesquioxane and 20ppm of platinum catalyst dissolved in a low molecular weight vinylpolymer were added to the blend to make the final composition. Thesilicone composition was coated onto a 20 cm×20 cm glass panel and curedat 120° C. for 30 minutes. Table 1 gives the ultra violet (UV) & Visual(V) light transmission data of a 200 μm film of this composition ascompared to commercial EVA film of the same thickness. The siliconecomposition shows a higher light transmission at 300 and 500 nm andsimilar transmission at 633 mm. The absorbed UV energy causes EVA toyellow and to brown and this effect is known to affect the visible lighttransmission.

TABLE 1 Comparative Ultraviolet and Visible light transmission as afunction of wavelength for EVA (ELVAX) and silicone material prepared inexample 1. % Transmittance 500 nm 400 mm 300 mm Samples Sample 633 nm(499.43) (400.20) (299.67) EVA1 (200 μm) 1 78 75 70 1 EVA3 (200 μm) 2 8583 80 0 EVA3 (200 μm) 3 85 83 80 1 Silicone material 1 84 83 81 73 200(μm) Silicone material 2 83 82 80 73 200 (μm)Values recorded here are lower than the actual due to the lightreflection effect on sample surface

Example 2 Silicone Composition that Exhibit Higher Taber AbrasionResistance than the ETFE/EVA Laminates

Film samples of similar composition as the one described in example 1were submitted to a Taber abrasion tester (Taber 5131 equipped withcalibrase CS-10 abrading wheels) while measuring the light transmissionchange as function of number of cycles. FIG. 1 indicates that after 40and 80 cycles, Tefzel® has lost 25% and 35% of the light transmissionrespectively while the silicone encapsulate of this invention has lostonly 8% of the light transmission after 100 cycles.

TABLE 2 % of light Transmission loss as a function of abrasion cycles(Taber 5131, Calibrase CS-10) (1): Tefzel ® 25 μm (2) and (3) siliconeencapsulant of this invention having 100 μm and 200 μm thickness. Alaminate of EVA/TEFZEL ® having 200 μm thickness did not show higherabrasion resistance than sample 1. Silicone Number of Tefzel ®Encapsulant Silicone encapsulant Cycles Thickness: 25 μm Thickness: 100μm Thickness: 200 μm 0 100 100 100 5 80.6 98.3 98.3 20 96.5 96.5 40 76.2— — 60 74.2 92.5 94.2 80 70.4 100 91.1 93.6

Example 3 Shore A Hardness of Cured Silicone Compositions in Accordancewith the Invention Showing a Gradient Toughness from the Surface to theBulk

Samples of similar composition as the one described in example 1 werecured in an aluminium cup to make 3 mm thick flat samples. The catalystconcentration was varied from 3.6 ppm to 7.1 ppm and the samples allowedto cure for 30 minutes at 120° C., FIG. 2 shows the variation ofhardness in shore A for both top surface and the bottom surface of thesample as a function of catalyst concentration. At 2.8 ppm, the sampleis skinned at the surface but do not fully cure. The example shows thatthe top surface is harder than the bottom surface indicating a faster orcomplete cure at the surface than in the bulk. The comparatively highhardness values indicate a high abrasion resistance and good surfaceproperties, while low hardness value (bottom surface) indicates softermaterial, good for cell protection. Hard material which is in contactwith a solar cell surface is likely to induce high stress at thecell/material surface and therefore a potential premature delamination,especially during thermal cycle change.

TABLE 3 Variation of Hardness as a function of platinum concentrationfor the top surface and the bottom surface of a silicone encapsulationof this invention cured in an aluminium cup. Hardness (Shore A) TopHardness (Shore A) Bottom Pt Catalyst Surface Surface 3.6 48.4 46.9 4.349.5 46.4 5 50.1 47.5 5.7 50.4 47.4 6.4 50.1 47.6 7.1 50.2 48

Example 4 Adhesion of the Encapsulant in Accordance with the Inventiononto a Glass Panel after Damp Heat Test

Samples of silicone encapsulant of similar composition as the onedescribed in example 1 were coated onto a 20 mm×20 mm glass panel tomake a 1000 μm thick layer. A 15 mm×15 mm silicon wafer of 650 μmthickness was immersed into the liquid encapsulant and then the assemblycured for 30 minutes at 120° C. The cured sample was submitted to ahumidity/temperature aging test (80° C./85% Relative Humidity (RH)) for41 days. No visible delamination could be observed, even after 60 days,the sample was still exhibiting a very good adhesion to the glass.

Example 5 Coating Glass Panels with a Modified Curtain Coater of thisInvention and Silicone Solar Encapsulant of this Invention

40 kg of the silicone encapsulant of this invention having a viscosityof 7000 mPa·s was fed into a curtain coater having 9 kg of polymer holdup and then pumped at 5.5 kg/min to make a nice curtain. 500×500 mmglass panels were fed continuously into the coater at 45 m/min to form apolymer film of 70 μm, after 6 passes under the curtain, a nice polymerfilm of 433 μm thickness was formed. The glass was then fed at 1 m/mininto a 1 meter long infrared oven equipped with four lamps of 1000 wattseach. The sample hardens rapidly to impart a high scratch resistancesurface to the glass surface.

Example 6 Coating Solar Glass Panels with a Modified Curtain Coater ofthis Invention and Silicone Solar Encapsulant of this Invention

Example 5 was repeated except that four interconnected solar cells weremanually glued on to the glass panels using a silicone base adhesivelayer of 100 μm. The solar glass with the interconnect on the top sidewas passed through the curtain at 20 m/min to make a top layer of 200μm, repeating the coating step once resulted in a solar panel coatedwith 400 μm encapsulating the interconnect. The top layer is thenhardened by passing it at 0.5 m/min in 0.8 m long Infrared tunnelequipped with 8 kW IR lamps from Heraeus.

Example 7 Encapsulation of a First Series of Interconnected CommerciallyAvailable a-Si Thin Film Cells with the Silicone Encapsulant of thePresent Invention

A glass substrate was initially cleaned using a suitable solvent, inthis case acetone and then the glass plate/thin film was treated withmethacrylopropyltrimethoxysilane and dried using compressed air. Theencapsulant used comprised 45 weight % of α,ω-dimethylvinylsiloxyterminated polydimethylsiloxane having a molecular weight of 62000g/mole and vinyl content of 0.15%; 18.6 weight % of trimethoxyterminated co polymer of dimethyl siloxane-co-methylhydrogensiloxanecontaining 1.45% of hydrogen units; 30.3 weight % (solids) of p-xylenesolution of dimethyl vinylated MQ resin (63% resin in Xylene) 5 weight %of adhesion promoter, 0.14 weight % of diallylmaleate cure inhibitor,0.11 weight % of platinum catalyst and 0.38 weight % of dimethylhydrogensiloxy terminated trifluoropropyl silsesquioxane.

The encapsulant was applied onto the module manually and afterlevelling, was cured in a standard oven at a temperature of 120° C. for20 mins.

The electrical capabilities were measured before and after the 10 dayaging process set down in the Humidity Freeze test described in IEC1646, which comprised 10 cycles of 24 hours with the temperature varyingfrom −40° C. to 85° C. in 85% relative Humidity (RH) and the results areprovided in Table 4 below

TABLE 4 Pmax delta (%)/ Name Pmax (W) previous meas. Control cell Samplebefore 5.389 conditioning Sample after 10 days 5.600 3.9% Sample Samplebefore 5.206 without conditioning frame Sample after 10 days 5.053 −2.9%conditioning Sample Sample before 4.979 with conditioning frame Sampleafter 10 days 4.908 −1.4% conditioning

None of the samples tested showed any discoloration or delamination andall samples passed the standard wet leakage current test as defined inthe IEC 1646 after the conditioning period.

In accordance with the requirements of IEC 1646 after conditioning asample should not show any open circuit or leakage current, any visualdefect and any decrease in maximum power should not be greater than 5%all of which the thin film modules of the present invention using theencapsulant alone (i.e. no adhesive layer required). These findings aretotally contrary to the expectations of the industry and use of asilicone encapsulant as hereinbefore described is able to provide thelevel of protection suitable for solar or photovoltaic module.

Example 8 Humidity Freeze Testing of a Different Series ofInterconnected Commercially Available a-Si Thin Film Cells

With the exception that the glass was washed with ethanol instead ofacetone and that a different type of commercially available solar cellwas used, the procedure followed was identical to the procedure inExample 7 above and as set down in IEC 1646.

Sample Characterization:

The electrical capabilities were measured before and after the 10 dayaging process set down in the Humidity Freeze test described in IEC1646, which comprised 10 cycles of 24 hours with the temperature varyingfrom −40° C. to 85° C. in 85% relative Humidity (RH) Electricalcharacterization of the samples were carried out both before and afterconditioning and the results are summarized in Table 5 below.

TABLE 5 Pmax Pmax delta (%)/ Description Conditioning (W) previous meas.Type a Reference Before conditioning 1.13 No conditioning After 10 days1.13 −0.4% Specimen 1a Before conditioning 1.11 Frame After 10 daysconditioning 1.153 4.3% Specimen 2a Before conditioning 1.21 No frameAfter 10 days conditioning 1.24 2.5% Type b Reference Beforeconditioning 1.14 After 10 days 1.12 −1.5% Specimen 1b Beforeconditioning 1.2 Frame After 10 days conditioning 1.16 −0.9% Specimen 2bBefore conditioning 1.25 Unframe After 10 days conditioning 1.25 −0.5%Type c Reference Before conditioning 1.13 After 10 days 1.14 0.4%Specimen 1c Before conditioning 1.11 Frame After 10 days conditioning1.12 0.9% Specimen 2c Before conditioning 1.15 Unframe After 10 daysconditioning 1.16 0.7% Type d Reference Before conditioning 1.20 After10 days 1.17 −2.3% Specimen 1d Before conditioning 1.17 Frame After 10days conditioning 1.15 −2.0% Specimen 2d Before conditioning 1.15Unframe After 10 days conditioning 1.16 1.3%

None of the samples tested showed any discoloration or delamination andall samples passed the standard wet leakage current test as defined inthe IEC 1646 after the conditioning period.

In accordance with the requirements of IEC 1646 after conditioning asample should not show any open circuit or leakage current, any visualdefect and any decrease in maximum power should not be greater than 5%all of which the thin film modules of the present invention using theencapsulant alone (i.e. no adhesive layer required).

These findings are totally contrary to the expectations of the industryand use of a silicone encapsulant as hereinbefore described is able toprovide the level of protection suitable for solar or photovoltaicmodule with both framed and unframed modules

Example 9 Encapsulation of p-Si Wafer Type 1 with Adhesive andEncapsulant

A glass substrate was initially cleaned using a suitable solvent, inthis case acetone and then the glass plate/thin film was treated withmethacrylopropyltrimethoxysilane and dried using compressed air. Theadhesive used comprised 27.5 weight % of α,ω-dimethylvinylsiloxyterminated polydimethylsiloxane having a viscosity of about 10 000mPa·s, molecular weight of 62000 g/mole and vinyl content of 0.15%; 45.8weight % of α,ω-dimethylvinylsiloxy terminated polydimethylsiloxanehaving a viscosity of about 450 mPa·s, 3 weight % of trimethoxyterminated co polymer of dimethyl siloxane-co-methylhydrogensiloxanecontaining 1.45% of hydrogen units; 18.3 weight % (solids) of p-xylenesolution of dimethyl vinylated MQ resin (63% resin in Xylene) 5 weight %of adhesion promoter, 0.24 weight % of diallylmaleate cure inhibitor,0.19 weight % of platinum catalyst.

The adhesive was cured in place using a hot plate by heating for 7 minat 120° C. or in a continuous process after application by a curtaincoater the adhesive was cured in the module in a Mid IR oven having atemperature profile of 120° C. and a speed of 0.5 m per minute for alength of 5 m.

The encapsulant composition was the same as detailed in Example 7.Encapsulant was applied onto the cured adhesive either manually in thelab or by means of a curtain coater. The encapsulant was cured in placeusing a hot plate by heating for 7 min at 120° C. or in a continuousprocess after application by a curtain coater the adhesive was cured inthe module in a Mid IR oven having a temperature profile of 120° C. anda speed of 0.5 m per minute for a length of 5 m.

The electrical capabilities were measured before and after the 10 dayaging process set down in the Humidity Freeze test described in IEC1215, which comprised 10 cycles of 24 hours with the temperature varyingfrom −40° C. to 85° C. in 85% relative Humidity (RH)

Sample Characterization:

Electrical characterization of the specimen has been done before andafter conditioning, results are summarized in table 6 below

TABLE 6 Pmax delta (5)/ Name Condition Pmax (W) previous meas. Sample 1Before conditioning 1.71 After 5 days conditioning 1.70 −0.5% After 10days conditioning 1.73 1.8% Sample 2 Before conditioning 1.29 After 5days conditioning 1.30 1.1% After 10 days conditioning 1.42 9.2% Sample3 Before conditioning 1.64 After 5 days conditioning 1.70 3.9% After 10days conditioning 1.75 2.9% Sample 4 Before conditioning 1.38 After 5days conditioning 1.40 1.2% After 10 days conditioning 1.51 7.9%

None of the samples were showing discoloration or delamination and werepassing the wet leakage current test as described in the IEC 1215 afterthe conditioning.

In accordance with the requirements of IEC 1215 after conditioning asample should not show any open circuit or leakage current, any visualdefect and any decrease in maximum power should not be greater than 5%all of which the thin film modules of the present invention using theencapsulant alone (i.e. no adhesive layer required). These findings aretotally contrary to the expectations of the industry and use of asilicone encapsulant as hereinbefore described is able to provide thelevel of protection suitable for solar or photovoltaic module of apolycrystalline Silicon wafer type.

Example 10 Encapsulation of Second Type Commercially Available p-SiWafer with Adhesive and Encapsulant

In this case the only difference from example 8 was the change in thesolar cells used. The adhesive and encapsulant compositions were asdescribed in example 8.

The electrical capabilities were measured before and after the 10 dayaging process set down in the Humidity Freeze test described in IEC1215, which comprised 10 cycles of 24 hours with the temperature varyingfrom −40° C. to 85° C. in 85% relative Humidity (RH)

The results are provided in Table 7 below

TABLE 7 Pmax delta (%)/ Name Condition Pmax (W) previous meas. Sample 1Before conditioning 1.70 After 5 days conditioning 1.70 0.0% After 10days conditioning 1.70 0.0% Sample 2 Before conditioning 1.70 After 5days conditioning 1.70 0.0% After 10 days conditioning 1.80 5.9% Sample3 Before conditioning 1.70 After 5 days conditioning 1.70 0.0% After 10days conditioning 1.80 5.9%

None of the samples were showing discoloration or delamination and werepassing the wet leakage current test as described in the IEC 1215 afterthe conditioning.

In accordance with the requirements of IEC 1215 after conditioning asample should not show any open circuit or leakage current, any visualdefect and any decrease in maximum power should not be greater than 5%all of which the thin film modules of the present invention using theencapsulant alone (i.e. no adhesive layer required). These findings aretotally contrary to the expectations of the industry and use of asilicone encapsulant as hereinbefore described is able to provide thelevel of protection suitable for solar or photovoltaic module of apolycrystalline Silicon wafer type.

Example 11 Coating Glass Panels with a Modified Curtain Coater of thisInvention and Silicone Solar Encapsulant of this Invention

40 Kg of the silicone encapsulant of this invention having a viscosityof 7000 mPa·s was fed into a curtain coater and was then pumped at 5.5Kg/min to make a suitable curtain. 500×500 mm glass panels were fedcontinuously into the coater at 45 m/min to form a polymer film of 70μm, after 6 passes under the curtain, an encapsulant film of 433 μmthickness was formed. The glass was then fed at 1 m/min into 1 meterlong infrared oven equipped with 4 lamps of 1000 watts each. Theencapsulant cured rapidly to impart a high scratch resistance surface tothe glass surface.

Example 12 Coating Solar Glass Panels with a Modified Curtain Coater ofthis Invention and Silicone Solar Encapsulant of this Invention

Example 11 was repeated except that 4 interconnected solar cells weremanually glued on to the glass panels by applying a layer of theadhesive having a thickness of 100 μm. The solar glass with theinterconnect on the top side was passed through the curtain at 20 m/minto make a top layer of 200 μm, repeating the coating step once resultedin a solar panel coated with 400 μm encapsulating the interconnect. Thetop layer was then cured by passing through a 0.8 m long Infrared tunnelequipped with 8 kW IR lamps from Heraeus it at a speed of 0.5 m/min.

Example 13

A series of standard electrical tests were carried out in respect towafer type modules encapsulated in accordance with the present inventionas compared to standard modules made with EVA/TEDLAR laminatetechnology. The modules made in accordance with the present inventioncomprised a float glass superstrate (size 200 mm×200 mm×3 mm) and asolar cell (size 125 mm×125 mm×350 μm) made from polycrystalline siliconwhich had been coated in silicon nitride. All modules tested wereframed, prior to the application of the adhesive layer, in the lab usingaluminium L-shaped profile frames in combination a suitable curablesealant adapted to seal the edges of the module and the frame. Eachframed module in accordance with the present invention was encapsulatedby first applying a layer of the silicone adhesive on to the glassplate. The solar cell (i.e. a silicon wafer) was then placed on to orinto the adhesive by a six axis robot to ensure that the cell wascorrectly positioned. The adhesive layer, containing/comprising the cellwas then cured using a hot plate. A layer of encapsulant was thenapplied on to the cured adhesive layer and subsequently cured in anoven. Encapsulated modules in accordance with the present invention weremade using the adhesive having a formulation as described in Example 9above and the encapsulant having a formulation as described in example 7above. The standard comparative solar cells were standard modules madewith EVA/TEDLAR laminate technology supported by tempered glasssuperstrates. The laminated modules were also framed as above usingidentical frames and sealant.

UV Conditioning

The UV conditioning test followed the Irradiation test A-5, p13”procedures set down in Japanese International standard Test “JIS C 8917Environmental and endurance test method for crystalline solar PV moduleswith reference to “JIS B 7753 Light-exposure andlight-and-water-exposure apparatus” describing the UV ageing conditions.A Xenon Lamp (Wavelength range: 340 nm) provided a continuous UVradiation at the surface of the sample: of 244.63 W/m² in 50% RelativeHumidity for 600 hours. The resulting aged modules were subsequentlyconditioned for 2 h at room temperature prior to testing. The sequenceof test performed followed JIS C 8917. The variation in electricalperformance of the modules between initial and post ageing are providedin Tables 8 (VA/TEDLAR® and 9 (present invention) in which the followingparameters are provided Temperature, Intensity of Short Circuit(Isc/Ampere(A)), Open circuit voltage (Voc), maximum voltage (Vmax),maximum current intensity (Imax), Fill factor, and maximum power. Inorder to pass the test each sequential test had to be achieved and thedifference between the initial and final Pmax had to be <5%.

Tables 8 and 9 show the relative changes (delta results) comparing theinitial and post ageing electrical performance of the standard modules(Table 8) and the modules in accordance with the present invention(Table 9).

TABLE 8 Delta results for EVA/Tedlar based solar modules after UV ageing600 h Δ Temp Δ ISC Δ Voc Δ Vmax Δ Imax Δ FF Δ Pmax EVA/Tedlar % % % (V)% (A) % (%) (W) Visuals Reference 0.7 −0.8 0.3 −1.0 0.5 −0.1 −0.5 OkComp A 1.1 −1.4 −0.3 −2.2 0.1 −0.3 −2.0 Ok Comp B 1.3 −0.9 0.7 −1.9 0.7−1.0 −1.2 Ok Mean % For 1.2 −1.15 0.2 −2.05 0.4 −0.65 −1.6 N/A Comps Aand B

TABLE 9 Delta results for Modules encapsulated in accordance with thepresent invention after UV ageing 600 h DC Encapsulant & Δ Temp Δ ISC ΔVoc Δ Vmax Δ Imax Δ FF Δ Pmax adhesive % % % (V) % (A) % (%) (W) VisualsEx Reference −1.3 −1.5 0.6 −2.3 0.1 −1.3 −2.3 Ok Ex A 0.4 −2.4 0.4 −2.30.03 0.3 −2.3 Ok Ex B 0.3 −1.9 0.7 −4.0 −0.1 −1.7 −2.3 Ok Ex C 0.02 −0.3−0.4 −0.4 −0.03 0.2 −0.5 Ok Mean % For 1.24 −1.53 0.23 −2.23 −0.03 −0.4−1.7 N/A Ex A, B, and C

The Reference and Ex Reference were aged under standard laboratoryconditions. Comp A and Comp B are seen to have lost more Power and FFthan the reference, however both passed the test by having less than 5%change after ageing.

Table 9 shows that all the samples in accordance with the presentinvention were encapsulated with no initial failure and passed the test.The loss in power is generally similar to the results for the Ex Refsample. In general all the samples submitted to the 600 h QUV ageing didnot lose their property at all compared to the reference.

Example 14 Thermal Cycling 50 Cycles+Humidity Freeze 10 Cycles Sequence

-   -   i) Initial and final Electrical performance results were        compared for a further series of modules of the types described        in example 13. The thermal cycling (50 cycles)+Humidity Freeze        (10 cycles) sequences were followed in accordance with IEEE        1262-1995 testing worksheet, p. 22. (and IEC 6-1215, and        UL1703).

Tables 10 and 11 provided the percentage changes in Pmax tested prior toand after ageing. Any loss in Pmax of more than 5% is considered afailure. This test subjects samples to ageing conditions which enablethe evaluation of the prospective ability of modules to withstandthermal expansion and contraction (through the thermal cycling) and toresist water penetration when submitted to extreme conditions oftemperature and humidity (Humidity Freeze).

Table 10 and 11 compare deltas results between the initial values andthe final ones for the standard EVA/TEDLAR® laminated solar modules(Table 10) and the solar modules encapsulated in accordance with thepresent invention.

TABLE 10 EVA/Tedlar deltas results after 50 Thermal Cycles + 10 cyclesHumidity Freeze conditions Δ Temp Δ ISC Δ Voc Δ Vmax Δ Imax Δ FF Δ PmaxEVA/Tedlar % % % (V) % (A) % (%) (W) % Reference 0.3 −0.9 −0.6 −2.1 −0.5−1.2 −2.2 Comp C −0.5 0.4 −1.4 −0.4 −0.7 0.0 −1.1 Comp D −0.1 −0.6 −1.5−1.4 −1.7 −1.1 −3.0 Comp E −0.7 −0.2 −1.5 −0.2 −0.1 1.5 −0.3 Mean % For−0.43 −0.13 −1.47 −0.67 −0.83 0.13 −1.47 Comps C, D, and E

TABLE 11 Encapsulant/adhesive in accordance with the present inventiondeltas results after 50 Thermal Cycles + 10 cycles Humidity Freezeconditions Encapsulant & Δ Temp Δ ISC Δ Voc Δ Vmax Δ Imax Δ FF Δ Pmaxadhesive % % % (V) % (A) % (%) (W) % Reference −1.4 −0.8 −0.8 −2.1 −0.4−0.9 −2.5 Ex D 0.5 −1.5 −0.2 −2.7 0.5 −0.5 −2.2 Ex E −0.3 −0.8 −0.7 −1.8−1.7 −2.5 −3.8 Ex F −0.3 −1.4 −0.2 −2.5 0.0 −0.9 −2.5 Mean % For −0.03−1.23 −0.37 −2.33 −0.40 −1.30 −2.83 Ex D, E, and F

In both Tables 10 and 11, the final electrical performance results areall deemed to pass the test (less than 5% change). Hence from the aboveit will be appreciated that use of an encapsulant and in the case ofthis example an adhesive as described in accordance with the presentinvention provides a simpler and continuous method of encapsulatingsolar cells as opposed to the traditional batch/lamination processes andthe resulting encapsulated solar modules give good electricalperformance results.

Example 15

Further samples as described in Example 13 were subjected to thesequence of test commonly referred to as Damp Heat Conditioning asdefined in each of IEC 6-1215, IEEE 1262, UL1703. The results providedin Tables 12 and 13 are determined by the relative percentage change ofinitial and final electrical test results. Any loss in Pmax of more than5% was deemed a failure. Tables 12 and 13 contrast the results betweenthe initial and the final electrical values ones for the twoencapsulation technologies.

TABLE 12 EVA/Tedlar deltas results after 1000 hours in Damp Heatconditions Δ Temp Δ ISC Δ Voc Δ Vmax Δ Imax Δ FF Δ Pmax EVA/Tedlar % % %(V) % (A) % (%) (W) % Reference 0.4 −2.0 0.2 −2.9 0.2 −0.9 −2.5 Comp F−0.1 −0.7 1.1 0.2 1.6 1.5 1.9 Comp G −1.1 −0.6 0.1 −1.4 0.1 −0.8 −1.2Comp H −0.8 −0.6 0.9 −0.6 0.4 −0.3 −0.2 Mean % For −0.67 −0.63 0.70−0.60 0.70 0.13 0.17 Comps F, G, and H

TABLE 13 Encapsulant/Adhesive deltas results after 1000 hours in DampHeat conditions Δ Temp Δ ISC Δ Voc Δ Vmax Δ Imax Δ FF Δ Pmax DCEncapsulant % % % (V) % (A) % (%) (W) % Reference −1.5 −2.2 −0.1 −2.90.0 −0.6 −2.9 Ex G −0.9 −1.6 −0.6 −1.6 −0.2 0.3 −1.9 Ex H −1.4 −1.8 −1.2−1.0 −0.2 1.8 −1.3 Ex I 0.1 −1.1 0.1 −2.1 −0.2 −1.2 −2.2 Mean % For Ex−0.73 −1.50 −0.57 −1.57 −0.20 0.30 −1.80 G, H, and I

Both tables 12 and 13 indicate that the changes in electrical propertiespass the test.

The invention claimed is:
 1. A solar cell module comprising: (1) a rigidor flexible superstrate; (2) a silicone adhesive disposed on saidsuperstrate and formed from a silicone adhesive composition that has aviscosity of from 100 to 2,000 mPa·s at 25° C. before curing andcomprises; (Ai) 100 parts by weight of a first liquiddiorganopolysiloxane having at least two Si-alkenyl groups per molecule,(Bi) 20 to 40 parts by weight of a first silicone resin containing atleast two alkenyl groups, (Ci) a first cross-linking agent in the formof a polyorganosiloxane having at least two silicon-bonded hydrogenatoms per molecule, in an amount such that the ratio of the number ofmoles of silicon-bonded hydrogen to the total number of moles ofsilicon-bonded alkenyl groups in component (Ai) is from 0.1:1 to 1:1,and (Di) a first hydrosilylation catalyst wherein the amount of metal insaid hydrosilylation catalyst is from 0.01 to 500 parts by weight per1,000,000 parts by weight of component (Ai); (3) one or more solar cellsdisposed on said silicone adhesive; and (4) a silicone encapsulantdisposed on said one or more solar cells and formed from a liquidsilicone encapsulant composition comprising; (A) 100 parts by weight ofa second liquid diorganopolysiloxane having at least two Si-alkenylgroups per molecule and a viscosity of from 100 to 10,000 mPa·s at 25°C., (B) 20 to 50 parts by weight of a second silicone resin containingat least two alkenyl groups, (C) a second cross-linking agent in theform of a polyorganosiloxane having at least two silicon-bonded hydrogenatoms per molecule, in an amount such that the ratio of the number ofmoles of silicon-bonded hydrogen to the total number of moles ofsilicon-bonded alkenyl groups in component (A) is >1:1, and (D) a secondhydrosilylation catalyst wherein the amount of metal in saidhydrosilylation catalyst is from 0.01 to 500 parts by weight per1,000,000 parts by weight of component (A).
 2. A solar cell module inaccordance with claim 1 wherein said one or more solar cells is either awafer or a thin film and is made from a semi-conductor material.
 3. Asolar cell module in accordance with claim 1 wherein said one or moresolar cells is a wafer and is made from a semi-conductor material thatis polycrystalline or single crystal silicon.
 4. A solar cell module inaccordance with claim 1 wherein said one or more solar cells is a thinfilm and is made from a semi-conductor material that is thin filmsilicon or copper indium gallium diselenide.
 5. A solar cell module inaccordance with claim 1 wherein the ratio of the number of moles ofsilicon-bonded hydrogen to the total number of moles of silicon-bondedalkenyl groups in component (A) of said liquid silicone encapsulantcomposition is from >1:1 to 5:1.
 6. A solar cell module in accordancewith claim 5 wherein said liquid silicone encapsulant compositionadditionally comprises one or more adhesion promoter(s) and/or ananti-soiling agent(s) and/or cure inhibitor(s) and/or a silane of theformula:(R¹O)₃SiR² wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms,R² is selected from the group of an alkoxy group comprising 1 to 6carbon atoms, an alkyl group comprising 1 to 6 carbon atoms, an alkenylgroup comprising 1 to 6 carbon atoms, an acrylic group or an alkylacrylic group.
 7. A solar cell module in accordance with claim 1 whereinthe ratio of the number of moles of silicon-bonded hydrogen to the totalnumber of moles of silicon-bonded alkenyl groups in component (Ai) is<1:1.
 8. A solar cell module in accordance with claim 1 wherein saidsilicone adhesive composition additionally comprises an adhesionpromoter and/or a cure inhibitor and/or a silane of the formula:(R¹O)₃SiR² wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms,R² is selected from the group of an alkoxy group comprising 1 to 6carbon atoms, an alkyl group comprising 1 to 6 carbon atoms, an alkenylgroup comprising 1 to 6 carbon atoms, an acrylic group or an alkylacrylic group.
 9. A solar cell module as set forth in claim 1 whereinsaid liquid silicone encapsulant composition comprises a resin fractionof between 30% and 50% by weight and said silicone adhesive compositioncomprises a resin fraction of between 20% and 30% by weight.
 10. A solarcell module in accordance with claim 9 wherein said liquid siliconeencapsulant composition cures without releasing volatiles.
 11. A solarcell module in accordance with claim 9 wherein said silicone encapsulantand/or silicone adhesive exhibits a light transmission substantiallyequivalent to glass.
 12. A solar cell module in accordance with claim 9wherein said one or more solar cells is pre-treated prior to adhesionand/or encapsulation with a silane of the formula:(R¹O)₃SiR² wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms,R² is selected from the group of an alkoxy group comprising 1 to 6carbon atoms, an alkyl group comprising 1 to 6 carbon atoms, an alkenylgroup comprising 1 to 6 carbon atoms, an acrylic group or an alkylacrylic group.
 13. A solar cell module in accordance with claim 2wherein said semi-conductor material is selected from the groupconsisting of crystalline silicon, polycrystalline silicon, singlecrystal silicon, thin film silicon, amorphous silicon, semi crystallinesilicon, gallium arsenide, copper indium diselenide, cadmium telluride,copper indium gallium diselenide, and mixtures thereof.
 14. A solar cellmodule in accordance with claim 1 wherein said liquid siliconeencapsulant composition cures without releasing volatiles.
 15. A solarcell module in accordance with claim 1 wherein said silicone encapsulantexhibits a light transmission substantially equivalent to glass.
 16. Asolar cell module in accordance with claim 1 wherein said one or moresolar cells is pre-treated prior to encapsulation with a silane of theformula:(R¹O)₃SiR² wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms,R² is selected from the group of an alkoxy group comprising 1 to 6carbon atoms, an alkyl group comprising 1 to 6 carbon atoms, an alkenylgroup comprising 1 to 6 carbon atoms, an acrylic group or an alkylacrylic group.
 17. A solar cell module in accordance with claim 1wherein said silicone adhesive exhibits a light transmissionsubstantially equivalent to glass.
 18. A solar cell module in accordancewith claim 1 that is free of ethylene-vinyl acetate (EVA) copolymer. 19.A module as set forth in claim 1 wherein each of said silicone adhesiveand said silicone encapsulant are free of ethylene-vinyl acetate (EVA)copolymer.
 20. A module as set forth in claim 1 wherein said siliconeencapsulant is an outermost layer of said module.
 21. A continuous solarcell module encapsulation process comprising the steps of uniformlyapplying by spraying, coating or dispensing a predetermined volume of asilicone adhesive composition onto a rigid or flexible superstrate,disposing one or more solar cells on the silicone adhesive composition,uniformly applying by spraying, coating or dispensing a predeterminedvolume of a liquid silicone encapsulant composition onto the one or moresolar cells and curing the silicone adhesive composition and the liquidsilicone encapsulant composition thermally or by infrared radiation,wherein the silicone adhesive composition has a viscosity of from 100 to2,000 mPa·s at 25° C. before curing and comprises: (Ai) 100 parts byweight of a first liquid diorganopolysiloxane having at least twoSi-alkenyl groups per molecule; (Bi) 20 to 40 parts by weight of a firstsilicone resin containing at least two alkenyl groups; (Ci) a firstcross-linking agent in the form of a polyorganosiloxane having at leasttwo silicon-bonded hydrogen atoms per molecule, in an amount such thatthe ratio of the number of moles of silicon-bonded hydrogen to the totalnumber of moles of silicon-bonded alkenyl groups in component (Ai) isfrom 0.1:1 to 1:1; and (Di) a first hydrosilylation catalyst wherein theamount of metal in the hydrosilylation catalyst is from 0.01 to 500parts by weight per 1,000,000 parts by weight of component (Ai); and thesilicone adhesive composition cures to form a silicone adhesive; whereinthe liquid silicone encapsulant composition comprises: (A) 100 parts byweight of a second liquid diorganopolysiloxane having at least twoSi-alkenyl groups per molecule and a viscosity of from 100 to 10,000mPa·s at 25° C.; (B) 20 to 50 parts by weight of a second silicone resincontaining at least two alkenyl groups; (C) a second cross-linking agentin the form of a polyorganosiloxane having at least two silicon-bondedhydrogen atoms per molecule, in an amount such that the ratio of thenumber of moles of silicon-bonded hydrogen to the total number of molesof silicon-bonded alkenyl groups in component (A) is >1:1; and (D) asecond hydrosilylation catalyst wherein the amount of metal in thehydrosilylation catalyst is from 0.01 to 500 parts by weight per1,000,000 parts by weight of component (A); and wherein the liquidsilicone encapsulant composition cures to form a silicone encapsulant.22. A continuous solar cell module encapsulation process in accordancewith claim 21 wherein the silicone adhesive composition and the liquidsilicone encapsulant composition are cured in a continuous oven.
 23. Acontinuous solar cell module encapsulation process in accordance withclaim 21 wherein the layer resulting from the liquid siliconeencapsulant composition is a uniform thin film coating having athickness ranging from 20 μm to 1200 μm.
 24. A continuous solar cellmodule encapsulation process in accordance with claim 21 wherein thesilicone adhesive composition is applied on to the rigid or flexiblesuperstrate and cured prior to the introduction of the liquid siliconeencapsulant composition.
 25. A continuous solar cell moduleencapsulation process in accordance with claim 21 wherein the means ofapplying the liquid silicone encapsulant composition is adapted suchthat the liquid silicone encapsulant composition is applied in a uniformbubble-free or substantially bubble-free film in the solar cell module.26. A continuous solar cell module encapsulation process in accordancewith claim 21 wherein the uniform application of the liquid siliconeencapsulant composition results in a layer of the liquid siliconeencapsulant composition and deposition of the one or more solar cellsinto the layer of the liquid silicone encapsulant composition is byautomatic placement.
 27. A continuous solar cell module encapsulationprocess in accordance with claim 21 wherein a thermoplastic orthermo-elastomeric material is applied to form a frame surrounding acured solar cell module to protect edges of the cured solar cell modulefrom water ingress.
 28. A continuous solar cell module encapsulationprocess in accordance with claim 21 wherein a silane of the formula:(R¹O)₃SiR² wherein R¹ is an alkyl group comprising 1 to 6 carbon atoms,R² is selected from the group of an alkoxy group comprising 1 to 6carbon atoms, an alkyl group comprising 1 to 6 carbon atoms an alkenylgroup comprising 1 to 6 carbon atoms, an acrylic group or an alkylacrylic group; is utilised to pre-treat the one or more solar cellsprior to adhesion and/or encapsulation.
 29. A continuous solar cellmodule encapsulation process in accordance with claim 21 wherein theliquid silicone encapsulant composition is applied using a curtaincoater.
 30. A continuous solar cell module encapsulation process inaccordance with claim 21 that is free of ethylene-vinyl acetate (EVA)copolymer.